Reagent strips which comprise one or more test areas capable of undergoing a color change in response to contact with a liquid specimen which may contain one or more constituents of interest have found wide acceptance, particularly in the clinical chemistry field, and have become an extremely useful tool aiding the physician in the diagnosis of disease. In order to afford precise quantitation of such color changes not possible when color comparisons are made with the naked eye, instruments employing reflectance photometry have been developed for reading test strip color changes. Such instruments determine with consistent accuracy the amount of color change, and hence the amount of the sample constituents of interest.
The commercially available strip reading instruments represent a clear advance in the art. However, the speed with which strips can be read therewith is not sufficient adequately to cope with the large numbers of specimens handled by clinical laboratories. This is because in the use of these instruments one strip must be inserted, read and removed from the instrument before the same series of steps can be performed on the next succeeding strip. Moreover, with certain instruments the speed of operation is limited by the requirement for precise placement of the strip in the instrument.
Automation of clinical laboratory procedures has provided significant improvement in the speed with which specimens can be processed. However, the automated instrumentation developed has thus far been limited to laboratory chemical analysis procedures involving the use of liquid reagents, and do not lend themselves to the automated reading of test strips. Representative of such chemical analyzer instruments are those disclosed in U.S. Pat. Nos. 3,578,412 and 4,269,803.
The '412 patent discloses horizontal rails 10 which are vertically reciprocable by a first doubleacting air cylinder 28, and horizontal serrated racks 14 which are horizontally reciprocable by a second double-acting air cylinder 34. Plastic multiple cavity liquid sample receptacles 18 are moved by this arrangement past a series of processing stations where various analytical steps are performed. The receptacles have downwardly facing cavity portions at each end, and when the rails 10 are lowered, each such cavity portion fits down over a tooth of a rack 14, necessitating the use of retainer flanges 48 and hold down members 46.
The '803 patent utilizes a ratchet type reciprocable shuttle block 52 having spring loaded fingers 60 for advancing analysis slides 18 along a track 25 past metering and analysis stations. The weight of the slides must be great enough or they must be held down positively by means not shown, to cause the fingers to be tilted downwardly against the bias of the loading springs (not shown) when the shuttle block undergoes retractile movement.